This invention relates to the preparation of coated or pre-sealed components and their installation and assembly. More specifically, the present invention relates to pre-treating or pre-sealing surfaces of aircraft structural components with a layer of sealant material.
It has recently been discovered that the corrosion protection and ease of processing and assembly of certain, aircraft structural components can be improved by pre-treating the components with an organic, corrosion-inhibiting coating material prior to installation. It had been the conventional practice to coat or seal such components with wet sealants that are known to require extensive and expensive special handling, especially with respect to their disposal. The pre-treatment or pre-coating method obviates the need and use of the wet sealants, reducing processing time and disposal costs.
According to an exemplary pre-treatment process, it has been the practice to pre-coat some types of fasteners in aircraft assemblies with organic phenolic coating materials to protect the base metal of the fasteners and surrounding adjacent structure against corrosion damage. In this usual approach, the fastener is first fabricated and then heat-treated to its required strength. After heat-treatment, the fastener is etched with a caustic soda bath or otherwise cleaned to remove any scale produced in the heat-treatment. The organic phenolic coating material, dissolved in a volatile carrier liquid, is applied to the fastener by spraying, dipping, or the like. The carrier liquid is allowed to evaporate. The coated fastener is then heated to an elevated temperature for a period of time to cure the phenolic coating; typically one hour at 400° F. The finished fastener is then ready to be used in the assembly of the airframe structure. Alternatively, the heat-treatment step and curing step can occur simultaneously. The details of these process methods are contained in U.S. Pat. Nos. 5,614,037, 5,858,133, 5,922,472, 5,944,918, 6,221,177, 6,274,200, and 6,403,230.
Because sealant materials are typically used at the interface of mating or faying surfaces between components that are to be assembled and must be rendered air-tight, water-tight, or fuel-tight, the sealant materials used to coat or pre-coat the faying surface of the components prior to assembly are desirably impermeable. Exemplary organic polyurethane sealant materials, such as those disclosed in U.S. Pat. Nos. 6,133,371, 6,315,300, and 6,499,745 are considered to be impermeable.
Impermeable sealant materials may be used with success but the restriction of only using impermeable sealant materials means that the choice of sealant materials might be inadvertently or unduly limited (i.e., not actually required for real-world application) and does not necessarily include those sealant materials with other superior properties, such as resistance to deterioration, resistance to solvent attack, and resistance to elevated or depressed temperatures. Such limitations are undesirable and unreasonable since it is equally as desirable to provide sealant materials with improved resistance to deterioration, resistance to solvent attack, and resistance to elevated or depressed temperatures other than the impermeable sealant materials currently available.